Reduction of the Optical Loss in the Multi-Cathode Structure Organic Light Emitting Device Using a Long Range Surface Plasmon

Akiyoshi Mikami

doi:10.4236/opj.2016.68b038

Abstract

Light extraction efficiency of organic light-emitting devices has improved by using a nano-sized multi-cathode structure consisting of semi-transparent metal and an optical compensation layer. From the detail optical calculation based on the multi-scale analysis including near-field optics, it was found that surface plasmon loss in the metal cathode is suppressed to less than 10% due to long range and short range surface plasmon coupling between both sides of metal cathode. Not less than 90% of optical power in the dipole emission can be successfully utilized as propagation light. Light extraction efficiency in a phosphorescent device has improved about twice by using the multi-cathode structure.

Highlights

Organic light-emitting devices (OLED) are widely recognized as a potential application for high quality flat panel displays and general lighting
We have recently found that a multi-cathode (MLC) structure consisting of semi-transparent metal, an optical compensation layer and high reflection metal makes it possible to achieve more than 50% in out-coupling efficiency by the combination of high refractive index layer
Huge loss due to surface plasmon (SP) coupling with metal cathode was converted to propagation wave such as waveguide and substrate modes

Summary

Introduction

Organic light-emitting devices (OLED) are widely recognized as a potential application for high quality flat panel displays and general lighting. The internal quantum efficiency of OLED has been achieved near 100% using phosphorescent materials with proper management of singlet and triplet excitons [1]. One of the reasons is quite a large losses induced by surface plasmon polariton which is direct interaction between a metal cathode and evanescent wave in near-field of vertical dipole emission [2]. It is clear that the light outcoupling behavior significantly changes with optical constants of materials and the device structure including substrate, electrode and passivation layers. We have recently found that a multi-cathode (MLC) structure consisting of semi-transparent metal, an optical compensation layer and high reflection metal makes it possible to achieve more than 50% in out-coupling efficiency by the combination of high refractive index layer

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Methods

Conclusion